Cold-gas refrigerator



June 6, 1967 A. A. DROS 3,323,314

COLDGAS REFRIGERATOR Filed Feb. 17, 1966 INVENTOR. ALBERT ADROS United States Patent Ofi ice 3,323,314 Patented June 6, 1967 3,323,314 CQLD-GAS REFRIGERATOR Albert August Dros, Emrnasingel, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 17, 1966, Ser. No. 528,232 Claims priority, application Netherlands, Mar. 10, 1965 6,503,020 4 Claims. (Cl. 62-6) This invention relates to cold-gas refrigerators of the two-piston type comprising at least one compression piston and at least one expansion piston which can reciprocate with a mutual phase difference and the centre lines of which are substantially coincident. Said pistons can vary through their adjacent surfaces the volumes of a compression space and an expansion space which spaces have different mean temperatures during operation and communicate with each other through at least one regenerator. The machine also includes at least one further expansion space of variable volume, which is connected to a portion of the connection between the first-mentioned expansion space and the compression space which lies between the coldest and the hottest end surfaces of the regenerator.

In a known machine of the kind to which the present invention relates, the volume of the further expansion space is varied by a separate piston. This has the disadvantage of an additional possibility of leakage, whilst also a complicated drive is required for causing the piston to move in the correct phase with the two other pistons. This in combination makes the known machine not particularly interesting in structural respect. A further disadvantage of this known machine is that much cold can leak away from the expansion space to the atmosphere.

A cold-gas refrigerator according to the invention has for its purpose to obviate the above-mentioned disadvantages and, to this end, is characterized in that during operation the expansion space has the lowest mean temperature and is situated farthest away in the interior of the machine as viewed in the direction of the centre line of the machine, the further expansion space or spaces surrounding the expansion piston so that these spaces are further remote from the expansion space as their temperatures are higher, the piston surfaces which can vary the volume of the further expansion space or spaces being connected to the expansion piston, the passage of the regenerator or regenerators in the connection between the expansion space and the compression space decreasing, as viewed in the direction of the expansion space, after each area where this connection is coupled to a further expansion space.

A two-piston cold-gas refrigerator is thus obtained having a plurality of expansion spaces without introducing additional movable parts. The loss of cold flowing from the expansion space to the atmosphere is limited due to the expansion space and the atmoshp-ere being separated by the further expansion spaces which have a low temperature but higher than that of the expansion space. The expansion piston is thus surrounded by a plurality of temperature levels which bridge, as it were, the very low temperature of expansion and the ambient temperature. The advantages of a two-piston cold-gas refrigerator, inter alia rectilinear paths of flow of the medium, are thus completely retained;

In another advantageous embodiment of the cold-gas refrigerator according to the invention, the expansion piston comprises a plurality of parts having diameters which decrease in the direction of the compression piston, the end surface of the final part of the expansion piston being capable of varying the volume of the expansion space, whilst each of the annular piston surfaces formed by the transition between two piston parts of different diameters can vary the volume of a further expansion space, the cyclindrical regenerator comprising the same number of parts as the expansion piston, which parts have decreasing diameters in the direction of the expansion space, the regenerator being connected to one of the further expansion spaces at each transition between two parts thereof.

A very simple construction is thus obtained in which the expansion space of the lowest temperature is situated farthest in the interior of the machine so that the loss of cold will be comparatively small.

Another advantageous embodiment of the cold-gas re frigerator according to the invention comprises an expansion cylinder with an expansion piston adapted to move therein and one or more cylinders parallel thereto and in each of which a further piston can move for varying a further expansion space, the expansion piston and the further pistons being connected together and the walls of each of the further expansion spaces being connected to the expansion cylinder in a thermally conductive manner.

In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which FIGURES 1, 2 and 3 show three embodiments of coldgas refrigerators of the two-piston type.

FIG. 1 shows cylinders 1 and 4 in which a compression 2 and an expansion piston 3 respectively can reciprocate. The compression and expansion pistons can move with a mutual phase difference, the compression piston 2 varying the volume of a compression space 5. The expansion piston 3 comprises two parts 6 and 7 of different diameters. Upon movement the end surface of part 6 varies the volume of an expansion space 8. An annular surface 9 formed by the transition between the two parts 6 and 7 varies the volume of a further expansion space 10. The expansion space 8 and the compression space 5 communicate with each other through a freezer 11, :a regenerator 12 and a cooler 13. The regenerator 12 comprises two parts 14 and 15 of diiferent diameters, the part 14 which is nearest to the expansion space having the smaller diameter. A plurality of ducts 16 which connect the further expansion space 10 to the regenerator are connected to the regenerator at the transition between the parts 14 and 15. Said ducts may be formed as a freezer over part of their length, which part is preferably connected to part 15 of the regenerator.

The principle of the operation of such a cold-gas refrigerator has been described in US. Patent 2,907,175. The expansion space 8 will have a very low temperature during operation and the further expansion space 10 will have a temperature lying between the temperature of compression and the temperature of the space 8. The cold produced in the further expansion space 10 serves to compensate for the losses of the regenerator occurring in the part 14 thereof.

It is thus rendered possible with a very simple construction to use a plurality of expansion spaces even in refrigerators of the two-piston types. An important advantage of the construction shown in FIG. 1 is that the coldest expansion space lies farthest remote in the machine. Between the expansion space 8 and the crank space there is the further expansion space 10 which also has a low temperature but higher than that of the expansion space 8 the leakage of cold from the space 8 to the crank space is thus greatly counteracted.

FIG. 2 shows a cold-gas refrigerator which is roughly identical with that of FIG. 1 except that the expansion piston now comprises three parts 6, 7 and 20. This results in two annular surfaces which can vary the volumes of the further expansion spaces and 21. The regenerator now also comprises three parts 14, and 22, and ducts 16 connected to the expansion space 10 are again provided at the transition between the parts 14 and 15. Further the expansion space 21 is connected through ducts 23 to the transition area between the parts 15 and 22 of the regenerator.

The expansion space 8 is thus thermally separated from the atmosphere by the temperature barriers formed by the expansion spaces 10 and 21. Leakage of cold is thus greatly counteracted.

FIG. 3 shows a cold-gas refrigerator of the two-piston type in which an expansion piston 36 connected through a yoke 40 to a rim of further expansion pistons 37. Each piston 37 is housed in a cylinder 41 which extends in parallel with a cylinder 42 in which the expansion piston 36 can move. The pistons 37 can vary the volumes of the further expansion spaces present in cylinder 41 which are connected through ducts 16 to part 15 of the regenerator. The cylinders 41 are connected to the cylinder 42, at 45, in a heat-conductive manner. Thus another zone is created between the expansion space 8 and the atmosphere, which zone is maintained at a temperature comprised between the temperature of expansion and the ambient temperature. Thus the loss of cold on the expansion space 8 to the atmosphere is counteracted.

If desired the cylinders 41 may have different lengths so that more than one temperature barrier is obtained.

As will be evident from the foregoing, the invention affords the possibility to manufacture a cold-gas refrigerator of a comparatively simple construction which combines the advantages of the two-piston type machine with the advantages of machines having a plurality of expansion spaces.

What is claimed is:

- 1. A cold-gas refrigerator of the two-piston type having a crankcase comprising at least one cylinder, at least one compression piston and at least one expansion piston reciprocating with a mutual phase difference and together with the cylinder defining a compression space and an expansion space, the center lines of said pistons being substantially coincident, said pistons being adapted to vary through their adjacent surfaces the volume of said compression and expansion spaces, said spaces having a different mean temperature, communicating means between said compression and expansion spaces including a regenerator, an additional expansion space of variable volume, means connecting said additional expansion space with the communicating means between said compression and expansion spaces which is located between the end surfaces of said regenerator, the expansion space having the lowest mean temperature being located further away from said crankcase than said additional expansion space, the latter surrounding said expansion piston, said expansion piston having surfaces which can vary the volume of said additional expansion space, and said regenerator having stepped portions with the smallest portion being closer to said expansion space.

2. A cold-gas refrigerator of the two-piston type as claimed in claim 1 wherein said expansion piston is stepped and the diameters of the parts thereof decrease in the direction of said compression piston, the end surface of the expansion piston part having the smallest diam eter being adapted to vary the volume of the expansion space, the surface at the stepped part of said expansion piston extending transversely to the longitudinal axis of said expansion piston being adapted to vary the volume of said additional expansion space, said regenerator also being stepped and having the same number of parts as said expansion piston, the diameters of said regenerator parts decreasing in the direction of said expansion space, said means connecting the additional expansion space with the communicating means between the said compression and expansion spaces is at the transition surface between parts of said stepped regenerator.

3. A cold-gas regenerator as claimed in claim 1 further comprising at least one additional cylinder extending parallel to said cylinder, an additional piston reciprocally mounted in said additional cylinder for varying a further expansion space, means connecting said expansion piston and additional piston, the walls of said further expansion space being connected to said cylinder in a heat conducting manner.

4. A cold-gas refrigerator of the two-piston type as claimed in claim 1 wherein said means connecting said additional expansion space with the communicating means between said compression and expansion spaces is a duct extending substantially parallel to said cylinder.

References Cited UNITED STATES PATENTS 3,147,600 9/1964 Malaker 626 3,151,466 10/1964 Hogan 62--6 3,200,201 l1/l965 Heuchling 626 WILLIAM J. WYE, Primary Examiner. 

1. A COLD-GAS REFRIGERATOR OF THE TWO-PISTON TYPE HAVING A CRANKCASE COMPRISING AT LEAST ONE CYLINDER, AT LEAST ONE COMPRESSION PISTON AND AT LEAST ONE EXPANSION PISTON RECIPROCATING WITH A MUTUAL PHASE DIFFERECE AND TOGETHER WITH THE CYLINDER DEFINING A COMPRESSION SPACE AND AN EXPANSION SPACE, THE CENTER LINES OF SAID PISTONS BEING SUBSTANTIALLY COINCIDENT, SAID PISTONS BEING ADAPTED TO VARY THROUGH THEIR ADJACENT SURFACES THE VOLUME OF SAID COMPRESSION AND EXPANSION SPACES, SAID SPACES HAVING A DIFFERENT MEAN TEMPERATURE, COMMUNICATING MEANS BETWEEN SAID COMPRESSION AND EXPANSION SPACES INCLUDING A REGENERATOR, AN ADDITIONAL EXPANSION SPACES INCLUDING VOLUME, MEANS CONNECTING SAID ADDITIONAL EXPANSION SPACE WITH THE COMMUNICATING MEANS BETWEEN SAID COMPRESSION AND EXPANSION SPACES WHICH IS LOCATED BETWEEN THE END SURFACES OF SAID REGENERATOR, THE EXPANSION SPACE HAVING THE LOWEST MEAN TEMPERATURE BEING LOCATED FURTHER AWAY FROM SAID CRANKCASE THAN SAID ADDITIONAL EXPANSION SPACE, THE LATTER SURROUNDING SAID EXPANSION PISTON, SAID EXPANSION PISTON HAVING SURFACES WHICH CAN VARY THE VOLUME OF SAID ADDITIONAL EXPANSION SPACE, AND SAID REGENERATOR HAVING STEPPED PORTIONS WITH THE SMALLEST PORTION BEING CLOSER TO SAID EXPANSION SPACE. 